Executing Multiple Instructions Multiple Data (&#39;MIMD&#39;) Programs on a Single Instruction Multiple Data (&#39;SIMD&#39;) Machine

ABSTRACT

Executing Multiple Instructions Multiple Data (‘MIMD’) programs on a Single Instruction Multiple Data (‘SIMD’) machine, the SIMD machine including a plurality of compute nodes, each compute node capable of executing only a single thread of execution, the compute nodes initially configured exclusively for SIMD operations, the SIMD machine further comprising a data communications network, the network comprising synchronous data communications links among the compute nodes, including establishing a SIMD partition comprising a plurality of the compute nodes; booting the SIMD partition in MIMD mode; executing by launcher programs a plurality of MIMD programs on compute nodes in the SIMD partition; and re-executing a launcher program by an operating system on a compute node in the SIMD partition upon termination of the MIMD program executed by the launcher program.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The field of the invention is data processing, or, more specifically,methods, apparatus, and products for executing Multiple InstructionsMultiple Data (‘MIMD’) programs on a Single Instruction Multiple Data(‘SIMD’) machine.

2. Description of Related Art

The development of the EDVAC computer system of 1948 is often cited asthe beginning of the computer era. Since that time, computer systemshave evolved into extremely complicated devices. Today's computers aremuch more sophisticated than early systems such as the EDVAC. Computersystems typically include a combination of hardware and softwarecomponents, application programs, operating systems, processors, buses,memory, input/output devices, and so on. As advances in semiconductorprocessing and computer architecture push the performance of thecomputer higher and higher, more sophisticated computer software hasevolved to take advantage of the higher performance of the hardware,resulting in computer systems today that are much more powerful thanjust a few years ago.

Parallel computing is an area of computer technology that hasexperienced advances. Parallel computing is the simultaneous executionof the same task (split up and specially adapted) on multiple processorsin order to obtain results faster. Parallel computing is based on thefact that the process of solving a problem usually can be divided intosmaller tasks, which may be carried out simultaneously with somecoordination. Parallel computing may be implemented in architecturesoptimized to execute in a mode of ‘Single Instruction, Multiple Data’(‘SIMD’) or in a mode of ‘Multiple Instruction, Multiple Data’ (‘MIMD’).This exact terminology, SIMD and MIMD, is from the well-known Flynn'staxonomy, a classification of computer architectures first described byMichael J. Flynn in 1966.

A MIMD machine is a computer in which multiple autonomous processorssimultaneously execute different instructions on different data.Distributed systems are generally recognized to be MIMDarchitectures—either exploiting a single shared memory space or adistributed memory space. Many common computer applications areimplemented with MIMD architectures, including, for example, mostaccounting programs, word processors, spreadsheets, database managers,browsers, web applications, other data communications programs, and soon.

A SIMD machine is a computer that exploits multiple data streams againsta single instruction stream to perform operations which may be naturallyparallelized. SIMD machines are ubiquitous on a small scale, in digitalspeech processors, graphics processors, and the like. In addition,however, SIMD machines also make up the largest, most powerful computersin the world. The BlueGene/L computer architecture, for example, isimplemented with a SIMD architecture. BlueGene/L installations representnine of the twenty-five most powerful computer installations in theworld—according to a current listing of the top 500 supercomputer sitespublished by the TOP500 Project. In fact, most, if not all, of the mostpowerful computers in the world today are SIMD machines.

SIMD machines execute parallel algorithms, typically includingcollective operations. A parallel algorithm can be split up to beexecuted a piece at a time on many different processing devices, andthen put back together again at the end to get a data processing result.Some algorithms are easy to divide up into pieces. Splitting up the jobof checking all of the numbers from one to a hundred thousand to seewhich are primes could be done, for example, by assigning a subset ofthe numbers to each available processor, and then putting the list ofpositive results back together. In this specification, the multipleprocessing devices that execute the individual pieces of a parallelprogram are referred to as ‘compute nodes.’ A SIMD machine is composedof compute nodes and other processing nodes as well, including, forexample, input/output (‘i/o’) nodes, and service nodes.

Parallel algorithms are designed also to optimize the datacommunications requirements among the nodes of a SIMD machine. There aretwo ways parallel processors communicate, shared memory or messagepassing. Shared memory processing needs additional locking technologyfor the data and imposes the overhead of additional processor and buscycles and also serializes some portion of the algorithm. Messagepassing processing uses high-speed data communications networks andmessage buffers, but this communication adds transfer overhead on thedata communications networks as well as additional memory need formessage buffers and latency in the data communications among nodes.Designs of SIMD machines use specially designed data communicationslinks so that the communication overhead will be small but it is theparallel algorithm that decides the volume of the traffic.

The large aggregation of data processing power represented by massivelyparallel SIMD machines is extremely attractive to MIMD applications. TheBlueGene/L architecture produces many teraflops per rack, has a largememory footprint, and low power consumption—all features which wouldmake it very useful if MIMD programs could be run on it. MIMDoperations, however, require a model that allows for independentprograms on each compute. Today the hardware and software for such SIMDmachines are designed only to support applications based on cooperatingnodes, purely parallel SIMD applications. Specialized memory sharing anddata communications technology in SIMD machines, which make the SIMDmachines so powerful, render such SIMD machines useless for MIMDapplications. In the BlueGene example, a processing error on one node ofa partition immediately terminates all data processing operations onevery compute node in the partition—a necessary requirement when all thecompute nodes are running the same SIMD application—but a disaster forMIMD operations.

SUMMARY OF THE INVENTION

Methods, apparatus, and computer program products are disclosed forexecuting MIMD programs on a SIMD machine, the SIMD machine including aplurality of compute nodes, each compute node capable of executing onlya single thread of execution, the compute nodes initially configuredexclusively for SIMD operations, the SIMD machine further comprising adata communications network, the network comprising synchronous datacommunications links among the compute nodes, including establishing aSIMD partition comprising a plurality of the compute nodes, the computenodes in the SIMD partition electronically isolated from compute nodesin other partitions of the SIMD machine and coupled to one anotherthrough links of the network for synchronous data communications forparallel SIMD operations among the compute nodes in the SIMD partition;booting the SIMD partition in MIMD mode, including: setting, inoperating systems on the compute nodes of the SIMD partition, flagsindicating MIMD operation; loading onto the compute nodes of the SIMDpartition a launcher program; initializing with link trainingsynchronous data communications among links of the network among computenodes in the SIMD partition; initializing, with a parallel processingbarrier, parallel operations among the compute nodes of the SIMDpartition, and executing a launcher program on each compute node in theSIMD partition; executing by launcher programs a plurality of MIMDprograms on two or more of the compute nodes in the SIMD partition,including replacing the launcher programs with the MIMD programs inprocess address space in computer memory of the compute nodes, each MIMDprogram autonomously executing different instructions on different data;and re-executing a launcher program by an operating system on a computenode in the SIMD partition upon termination of the MIMD program executedby the launcher program.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescriptions of exemplary embodiments of the invention as illustrated inthe accompanying drawings wherein like reference numbers generallyrepresent like parts of exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary system for executing MIMD programs on aSIMD machine according to embodiments of the present invention.

FIG. 2 sets forth a block diagram of an exemplary compute node useful inexecuting MIMD programs on a SIMD machine according to embodiments ofthe present invention.

FIG. 3A illustrates an exemplary Point To Point Adapter useful insystems that execute MIMD programs on a SIMD machine according toembodiments of the present invention.

FIG. 3B illustrates an exemplary Collective Operations Adapter useful insystems that execute MIMD programs on a SIMD machine according toembodiments of the present invention.

FIG. 4 illustrates an exemplary data communications network optimizedfor point to point operations, useful in systems that executing MIMDprograms on a SIMD machine.

FIG. 5 illustrates an exemplary data communications network optimizedfor collective operations, useful in systems that executing MIMDprograms on a SIMD machine.

FIG. 6 sets forth a functional block diagram illustrating an exemplarysystem for executing MIMD programs on a SIMD machine according toembodiments of the present invention.

FIG. 7 sets forth a functional block diagram illustrating a furtherexemplary system for executing MIMD programs on a SIMD machine accordingto embodiments of the present invention.

FIG. 8 sets forth a flow chart illustrating an exemplary method ofexecuting MIMD programs on a SIMD machine according to embodiments ofthe present invention.

FIG. 9 sets forth a flow chart illustrating a further exemplary methodof executing MIMD programs on a SIMD machine according to embodiments ofthe present invention.

FIG. 10 sets forth a flow chart illustrating a further exemplary methodof executing MIMD programs on a SIMD machine according to embodiments ofthe present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary methods, apparatus, and computer program products forexecuting Multiple Instructions Multiple Data (‘MIMD’) programs on aSingle Instruction Multiple Data (‘SIMD’) machine according toembodiments of the present invention are described with reference to theaccompanying drawings, beginning with FIG. 1. FIG. 1 illustrates anexemplary system for executing MIMD programs on a SIMD machine accordingto embodiments of the present invention. The system of FIG. 1 includes aSIMD machine (100), a computer configured for exclusively parallel,collective operations. The system of FIG. 1 also includes non-volatilememory for the SIMD machine in the form of data storage device (118), anoutput device for the SIMD machine in the form of printer (120), and aninput/output (‘i/o’) device for the SIMD machine in the form of computerterminal (122). The SIMD machine (100) in the example of FIG. 1 includesa plurality of compute nodes (102), each of which is capable ofexecuting only a singe thread of execution.

The compute nodes (102) are coupled for data communications by severalindependent data communications networks including:

-   -   a high speed Ethernet network (174) that connects peripherals        through i/o node to compute nodes,    -   a Joint Test Action Group (‘JTAG’) network (104) for out of band        signaling between service nodes, i/o nodes, and compute nodes,    -   a synchronous collective network (106) in which each compute        node connects in a tree structure to three neighboring compute        nodes, with the collective network optimized for massively        parallel collective operations among compute nodes,    -   a synchronous point-to-point network (108), optimized for point        to point operations among compute nodes, in which each compute        node connects in a torus to six neighboring compute nodes        through which each node in the torus can communicate directly or        indirectly with every other compute node in the torus, and    -   a barrier network (109) connecting all compute nodes in an        independent network in which each compute node can signal to all        other compute nodes processing arrival at a parallel processing        barrier, halting further processing until all nodes have        reported arrival at the barrier.

Each data communications network is implemented with data communicationslinks among the compute nodes (102). The data communications linksprovide data communications for parallel operations among the computenodes of the SIMD machine. Point-to-point network (108) is a synchronousdata communications network that includes synchronous datacommunications links connected among the compute nodes so as to organizethe compute nodes in a mesh or torus. Collective network (106) is asynchronous data communications network that includes synchronous datacommunications links connected among the compute nodes so as to organizethe compute nodes in a tree structure.

The compute nodes may be organized in one or more SIMD partitions (133),or the SIMD machine may be booted without partitions, so that all thecompute nodes in the SIMD machine operate as one large operational groupfor parallel, collective operations on SIMD programs. A SIMD partitionis an operational group of compute nodes for collective paralleloperations on a SIMD machine (100). A SIMD partition is a set of computenodes upon which parallel collective operations of a SIMD applicationexecute. Such a SIMD partition may include all the compute nodes in aSIMD machine (100) or a subset all the compute nodes. The compute nodesin a SIMD partition are electronically isolated from compute nodes inother partitions of the SIMD machine. The compute nodes in a SIMDpartition are coupled to one another through links of at least onenetwork for synchronous data communications for parallel SIMD operationsamong the compute nodes in the SIMD partition.

Such collective operations are implemented with data communicationsamong the compute nodes of a SIMD partition. Collective operations arethose functions that involve all the compute nodes of an operationalgroup in parallel operations. A collective operation is an operation, amessage-passing computer program instruction that is executedsynchronously, that is, at approximately the same time, by all thecompute nodes in a SIMD partition. Such synchronous operations aresupported by synchronous data communications networks and parallelprocessing barriers. Parallel collective operations can be implementedwith point to point operations. A collective operation requires that allprocesses on all compute nodes within a SIMD partition call the samecollective operation with matching arguments. A ‘broadcast’ is anexample of a collective operations for moving data among compute nodesof a SIMD partition. A ‘reduce’ operation is an example of a collectiveoperation that executes arithmetic or logical functions on datadistributed among the compute nodes of a SIMD partition. A SIMDpartition may be implemented as, for example, an MPI ‘communicator.’

‘MPI’ refers to ‘Message Passing Interface,’ a parallel communicationslibrary, a module of computer program instructions for datacommunications on parallel computers. Examples of parallelcommunications libraries that may be useful or may be improved to beuseful for executing MIMD programs on a SIMD machine according toembodiments of the present invention include MPI and the ‘ParallelVirtual Machine’ (‘PVM’) library. PVM was developed by the University ofTennessee, The Oak Ridge National Laboratory and Emory University. MPIis promulgated by the MPI Forum, an open group with representatives frommany organizations that define and maintain the MPI standard. MPI at thetime of this writing is a de facto standard for communication amongcompute nodes running a parallel program on a distributed memoryparallel computer. This specification sometimes uses MPI terminology forease of explanation, although the use of MPI as such is not arequirement or limitation of the present invention.

Most collective operations are variations or combinations of four basicoperations: broadcast, gather, scatter, and reduce. In a broadcastoperation, all processes specify the same root process, whose buffercontents will be sent. Processes other than the root specify receivebuffers. After the operation, all buffers contain the message from theroot process.

A scatter operation, like the broadcast operation, is also a one-to-manycollective operation. All processes specify the same receive count. Thesend arguments are only significant to the root process, whose bufferactually contains sendcount*N elements of a given datatype, where N isthe number of processes in the given SIMD partition. The send bufferwill be divided equally and dispersed to all processes (includingitself). Each compute node in the SIMD partition is assigned asequential identifier termed a ‘rank.’ After the operation, the root hassent sendcount data elements to each process in increasing rank order.Rank 0 receives the first sendcount data elements from the send buffer.Rank 1 receives the second sendcount data elements from the send buffer,and so on.

A gather operation is a many-to-one collective operation that is acomplete reverse of the description of the scatter operation. That is, agather is a many-to-one collective operation in which elements of adatatype are gathered from the ranked compute nodes into a receivebuffer in a root node.

A reduce operation is also a many-to-one collective operation thatincludes an arithmetic or logical function performed on two dataelements. All processes specify the same ‘count’ and the same arithmeticor logical function. After the reduction, all processes have sent countdata elements from computer node send buffers to the root process. In areduction operation, data elements from corresponding send bufferlocations are combined pair-wise by arithmetic or logical operations toyield a single corresponding element in the root process's receivebuffer. Application specific reduction operations can be defined atruntime. Parallel communications libraries may support predefinedoperations. MPI, for example, provides the following pre-definedreduction operations:

MPI_MAX maximum MPI_MIN minimum MPI_SUM sum MPI_PROD product MPI_LANDlogical and MPI_BAND bitwise and MPI_LOR logical or MPI_BOR bitwise orMPI_LXOR logical exclusive or MPI_BXOR bitwise exclusive or

In addition to compute nodes, SIMD machine (100) includes input/output(‘I/O’) nodes (110, 114) coupled to compute nodes (102) through one ofthe data communications networks (174). The I/O nodes (110, 114) provideI/O services between compute nodes (102) and I/O devices (118, 120,122). I/O nodes (110, 114) are connected for data communications I/Odevices (118, 120, 122) through local area network (‘LAN’) (130).

The SIMD machine (100) also includes a service node (116) coupled to thecompute nodes through one of the networks (104). Service node (116)provides services common to pluralities of compute nodes, loadingprograms into the compute nodes, starting program execution on thecompute nodes, retrieving results of program operations on the computernodes, and so on. Service node (116) runs service applications (143) andcommunicates with users (128) through a service application interface(126) that runs on computer terminal (122). Service applications (143)that execute on the service node (116) include:

-   -   a control application (124), which is a module of computer        program instructions that boots partitions, loads launcher        programs onto compute nodes in SIMD partitions booted in MIMD        mode, and administers error conditions detected on compute        nodes,    -   a scheduler (140), which is a module of computer program        instructions that schedules data processing jobs on the SIMD        machine, including installing SIMD programs on compute nodes and        passing MIMD jobs along to a MIMD dispatcher for installation on        SIMD partitions booted in MIMD mode; and    -   a MIMD dispatcher (139), which is a module of computer program        instructions that installs MIMD programs on compute nodes in        SIMD partitions booted in MIMD mode.

In the example of FIG. 1, all the compute nodes (102) are initiallyconfigured exclusively for SIMD operations, and the system of FIG. 1operates generally to execute MIMD programs (158) on a SIMD machine(100) according to embodiments of the present invention by establishinga SIMD partition (133) comprising a plurality of the compute nodes(102); booting the SIMD partition (133) in MIMD mode; executing bylauncher programs (135) a plurality of MIMD programs (158) on two ormore of the compute nodes (102) in the SIMD partition (133); andre-executing a launcher program (135) by an operating system on acompute node in the SIMD partition upon termination of the MIMD programexecuted by the launcher program. Each MIMD program (158) is a module ofcomputer program instructions that autonomously executes differentinstructions on different data. That is, each MIMD program has computerprogram instructions that typically are not the same instructionsexecuted by other MIMD programs, and each MIMD program operates on datathat typically is not the same data processed by other MIMD programs.Booting the SIMD partition (133) in MIMD mode includes setting, inoperating systems on the compute nodes of the SIMD partition, flagsindicating MIMD operation; loading onto the compute nodes of the SIMDpartition a launcher program; initializing with link trainingsynchronous data communications among links of the network among computenodes in the SIMD partition; initializing, with a parallel processingbarrier, parallel operations among the compute nodes of the SIMDpartition; and executing a launcher program on each compute node in theSIMD partition.

A launcher program (135) is a module of computer program instructionsthat runs on a compute node in a SIMD partition booted in MIMD mode,receives from a MIMD dispatcher a name of a MIMD program, and executesthe MIMD program on the compute node. A launcher program may beimplemented, for example, as illustrated by these computer programinstructions:

launcher(dispatcherNetworkAddress) {   socketID = socket( );  connect(socketID, dispatcherNetworkAddress);   read(socketID,MIMDProgramName);   close(socketID);   exec(MIMDProgramName); }

This example launcher program is ‘pseudocode,’ an explanation set forthin code form, not an actual working model. As shown in this example, thelauncher programs typically use a Unix-like execo function to executeMIMD programs, so that executing MIMD programs replaces the launcherprogram with the MIMD program in process address space in computermemory of the compute node. Each compute node operates single-threaded,with only one thread of execution on the node. When a launcher programexecutes a MIMD program, the MIMD program, as a new thread of executionon a compute node that only supports one thread of execution, is writtenover the launcher program in the compute node's process address space,wiping out the launcher program. The operating system on the computenode therefore re-executes a launcher program on the compute node in theSIMD partition upon termination of the MIMD program earlier executed bya launcher program.

The arrangement of nodes, networks, and I/O devices making up theexemplary system illustrated in FIG. 1 are for explanation only, not forlimitation of the present invention. Data processing systems capable ofexecuting MIMD programs on a SIMD machine according to embodiments ofthe present invention may include additional nodes, networks, devices,and architectures, not shown in FIG. 1, as will occur to those of skillin the art. The SIMD machine (100) in the example of FIG. 1 includessixteen compute nodes (102)—whereas SIMD machines capable of executingMIMD programs according to embodiments of the present inventionsometimes include thousands of compute nodes. In addition to Ethernetand JTAG, networks in such data processing systems may support many datacommunications protocols including for example TCP (Transmission ControlProtocol), IP (Internet Protocol), and others as will occur to those ofskill in the art. Various embodiments of the present invention may beimplemented on a variety of hardware platforms in addition to thoseillustrated in FIG. 1.

Executing MIMD programs on a SIMD machine according to embodiments ofthe present invention is generally implemented on a parallel computerthat includes a plurality of compute nodes. In fact, such computers mayinclude thousands of such compute nodes. Each compute node is in turnitself a kind of computer composed of one or more computer processors,its own computer memory, and its own input/output adapters. For furtherexplanation, therefore, FIG. 2 sets forth a block diagram of anexemplary compute node useful for executing MIMD programs on a SIMDmachine according to embodiments of the present invention. The computenode (152) of FIG. 2 includes at least one computer processor (164) aswell as random access memory (‘RAM’) (156). Processor (164) is connectedto RAM (156) through a high-speed memory bus (154) and to othercomponents of the compute node through a bus adapter (194) and anextension bus (168).

Stored in RAM (156) is a parallel communications library (160), alibrary of computer program instructions that carry out parallelcommunications among compute nodes, including point to point operationsas well as collective operations.

Application program (158) executes collective operations by callingsoftware routines in parallel communications library (160). A library ofparallel communications routines may be developed from scratch for usein executing MIMD programs on a SIMD machine according to embodiments ofthe present invention, using a traditional programming language such asthe C programming language, and using traditional programming methods towrite parallel communications routines that send and receive data amongnodes on two independent data communications networks. Alternatively,existing prior art libraries may be used. Examples of parallelcommunications libraries that may be used or improved for use inexecuting MIMD programs on a SIMD machine according to embodiments ofthe present invention include the ‘Message Passing Interface’ (‘MPI’)library and the ‘Parallel Virtual Machine’ (‘PVM’) library.

Also stored in RAM (156) is an operating system (162), a module ofcomputer program instructions and routines for an application program'saccess to other resources of the compute node. It is typical for anapplication program and parallel communications library in a computenode of a SIMD machine to run a single thread of execution with no userlogin and no security issues because the thread is entitled to completeaccess to all resources of the node. The quantity and complexity oftasks to be performed by an operating system on a compute node in a SIMDmachine therefore are smaller and less complex than those of anoperating system on a serial computer with many threads runningsimultaneously. In addition, there is no video I/O on the compute node(152) of FIG. 2, another factor that decreases the demands on theoperating system. The operating system may therefore be quitelightweight by comparison with operating systems of general purposecomputers, a pared down version as it were, or an operating systemdeveloped specifically for operations on a particular SIMD machine.Operating systems that may usefully be improved, simplified, for use ina compute node for executing MIMD programs on a SIMD machine includeUNIX™, Linux™, Microsoft XP™, AIX™, IBM's i5/OS™, and others as willoccur to those of skill in the art.

Also stored in RAM (156) is a MIMD program (158), a module of computerprogram instructions that implements multiple-instruction, multiple dataprocessing. Also stored in RAM is a launcher program (135), a module ofcomputer program instructions that runs on the compute node (152) in aSIMD partition booted in MIMD mode, receives from a MIMD dispatcher aname of a MIMD program (158), and executes the MIMD program (158) on thecompute node (152). The launcher program (135) in this example is showndisposed in the RAM space of the operating system (162), presumablyhaving executed the MIMD program (158), which is shown here disposed inprocess address space (134), having wiped the launcher program out ofthe process address space (134) when the launcher program executed theMIMD program.

Also stored in RAM (156) is a MIMD flag (136), a Boolean data elementwhich when set to TRUE advises the operating system that the computenode is running in MIMD mode, so that upon termination of the MIMDprogram, the operating system, rather than terminating its ownoperations as it would do if it were operating in purely SIMD mode, nowre-executes the launcher program (135). And the compute node operatesgenerally as follows:

-   -   the launcher program connects to a dispatcher,    -   the launcher programs receives a MIMD program name from the        dispatcher,    -   the launcher program executes the MIMD program when provided        with the program name, installing the MIMD program in process        address space in RAM and wiping out the launcher program,    -   the operating system re-executes the launcher program upon        termination of the MIMD program,    -   and so on, repeating indefinitely.

The MIMD flag advises the operating system to reload the launcherprogram when the MIMD program exits—without notifying the controlapplication (124 on FIG. 1) of the exit. In effect, compared to SIMDoperations, the MIMD mode compute node never exits. It just reloads thelauncher program and waits for another MIMD program name to execute.

Also stored in RAM (156) is a reboot flag (137), a Boolean data elementwhich when set to TRUE advises the operating system (162) that a currentboot of the operating system is a reboot, that is, that the compute nodehas already been booted at least once before as part of a SIMD partitionbooted in MIMD mode. Remember that the overall undertaking here isexecuting a MIMD program on a SIMD machine where, in fact, the SIMDmachine remains a SIMD machine. In its inception, therefore, a boot of aSIMD partition in MIMD mode is still a boot of a SIMD partition. Theboot process is modified by inclusion of a launcher program, a MIMDflag, a reboot flag, and so on, but the underlying process is a SIMDboot. The original boot, therefore, includes SIMD-type functions thatare not needed on a reboot. Examples of such SIMD-type functions includeinitializing with link training synchronous data communications amonglinks of the network among compute nodes in the SIMD partition andinitializing, with a parallel processing barrier, parallel operationsamong the compute nodes of the SIMD partition. Such SIMD-type functionsare not needed on a reboot because, for example, the data communicationslinks are already trained for synchronous operation, and there is noneed to initialize parallel processing with a parallel processingbarrier because, at the time of a reboot, there is no longer anyparallel processing in the SIMD partition booted in MIMD mode. Theoperating system (162), advised to do so by a reboot flag (137) set toTRUE, upon a reboot, omits from the boot process the initializing ofsynchronous data communications on the network with link training andthe initializing of parallel operations among the compute nodes with aparallel processing barrier.

The exemplary compute node (152) of FIG. 2 includes severalcommunications adapters (172, 176, 180, 188) for implementing datacommunications with other nodes of a SIMD machine. Such datacommunications may be carried out serially through RS-232 connections,through external buses such as USB, through data communications networkssuch as IP networks, and in other ways as will occur to those of skillin the art. Communications adapters implement the hardware level of datacommunications through which one computer sends data communications toanother computer, directly or through a network. Examples ofcommunications adapters useful in systems that execute MIMD programs ona SIMD machine according to embodiments of the present invention includemodems for wired communications, Ethernet (IEEE 802.3) adapters forwired network communications, and 802.11b adapters for wireless networkcommunications.

The data communications adapters in the example of FIG. 2 include aGigabit Ethernet adapter (172) that couples example compute node (152)for data communications to a Gigabit Ethernet (174). Gigabit Ethernet isa network transmission standard, defined in the IEEE 802.3 standard,that provides a data rate of 1 billion bits per second (one gigabit).Gigabit Ethernet is a variant of Ethernet that operates over multimodefiber optic cable, single mode fiber optic cable, or unshielded twistedpair.

The data communications adapters in the example of FIG. 2 includes aJTAG Slave circuit (176) that couples example compute node (152) fordata communications to a JTAG Master circuit (178). JTAG is the usualname used for the IEEE 1149.1 standard entitled Standard Test AccessPort and Boundary-Scan Architecture for test access ports used fortesting printed circuit boards using boundary scan. JTAG is so widelyadapted that, at this time, boundary scan is more or less synonymouswith JTAG. JTAG is used not only for printed circuit boards, but alsofor conducting boundary scans of integrated circuits, and is also usefulas a mechanism for debugging embedded systems, providing a convenient“back door” into the system. The example compute node of FIG. 2 may beall three of these: It typically includes one or more integratedcircuits installed on a printed circuit board and may be implemented asan embedded system having its own processor, its own memory, and its ownI/O capability. JTAG boundary scans through JTAG Slave (176) mayefficiently configure processor registers and memory in compute node(152) for use in executing MIMD programs on a SIMD machine according toembodiments of the present invention.

The data communications adapters in the example of FIG. 2 includes aPoint To Point Adapter (180) that couples example compute node (152) fordata communications to a network (108) that is optimal for point topoint message passing operations such as, for example, a networkconfigured as a three-dimensional torus or mesh. Point To Point Adapter(180) provides data communications in six directions on threecommunications axes, x, y, and z, through six bidirectional links: +x(181), −x (182), +y (183), −y (184), +z (185), and −z (186).

The data communications adapters in the example of FIG. 2 includes aCollective Operations Adapter (188) that couples example compute node(152) for data communications to a network (106) that is optimal forcollective message passing operations such as, for example, a networkconfigured as a binary tree. Collective Operations Adapter (188)provides data communications through three bidirectional links: two tochildren nodes (190) and one to a parent node (192).

Example compute node (152) includes two arithmetic logic units (‘ALUs’).ALU (166) is a component of processor (164), and a separate ALU (170) isdedicated to the exclusive use of collective operations adapter (188)for use in performing the arithmetic and logical functions of reductionoperations. Computer program instructions of a reduction routine inparallel communications library (160) may latch an instruction for anarithmetic or logical function into instruction register (169). When thearithmetic or logical function of a reduction operation is a ‘sum’ or a‘logical or,’ for example, collective operations adapter (188) mayexecute the arithmetic or logical operation by use of ALU (166) inprocessor (164) or, typically much faster, by use of dedicated ALU(170).

For further explanation, FIG. 3A illustrates an exemplary Point To PointAdapter (180) useful in systems that execute MIMD programs on a SIMDmachine according to embodiments of the present invention. Point ToPoint Adapter (180) is designed for use in a data communications networkoptimized for point to point operations, a network that organizescompute nodes in a three-dimensional torus or mesh. Point To PointAdapter (180) in the example of FIG. 3A provides data communicationalong an x-axis through four unidirectional data communications links,to and from the next node in the −x direction (182) and to and from thenext node in the +x direction (181). Point To Point Adapter (180) alsoprovides data communication along a y-axis through four unidirectionaldata communications links, to and from the next node in the −y direction(184) and to and from the next node in the +y direction (183). Point ToPoint Adapter (180) in also provides data communication along a z-axisthrough four unidirectional data communications links, to and from thenext node in the −z direction (186) and to and from the next node in the+z direction (185).

For further explanation, FIG. 3B illustrates an exemplary CollectiveOperations Adapter (188) useful in systems that execute MIMD programs ona SIMD machine according to embodiments of the present invention.Collective Operations Adapter (188) is designed for use in a networkoptimized for collective operations, a network that organizes computenodes of a SIMD machine in a binary tree. Collective Operations Adapter(188) in the example of FIG. 3B provides data communication to and fromtwo children nodes through four unidirectional data communications links(190). Collective Operations Adapter (188) also provides datacommunication to and from a parent node through two unidirectional datacommunications links (192).

For further explanation, FIG. 4 illustrates an exemplary datacommunications network optimized for point to point operations (106). Inthe example of FIG. 4, dots represent compute nodes (102) of a SIMDmachine, and the dotted lines between the dots represent datacommunications links (103) between compute nodes. The datacommunications links are implemented with point to point datacommunications adapters similar to the one illustrated for example inFIG. 3A, with data communications links on three axes, x, y, and z, andto and fro in six directions +x (181), −x (182), +y (183), −y (184), +z(185), and −z (186). The links and compute nodes are organized by thisdata communications network optimized for point to point operations intoa three dimensional mesh (105) that wraps around to form a torus (107).Each compute node in the torus has a location in the torus that isuniquely specified by a set of x, y, z coordinates. For clarity ofexplanation, the data communications network of FIG. 4 is illustratedwith only 27 compute nodes, but readers will recognize that a datacommunications network optimized for point to point operations for usein executing MIMD programs on a SIMD machine in accordance withembodiments of the present invention may contain only a few computenodes or may contain thousands of compute nodes.

For further explanation, FIG. 5 illustrates an exemplary datacommunications network (108) optimized for collective operations byorganizing compute nodes in a tree. The example data communicationsnetwork of FIG. 5 includes data communications links connected to thecompute nodes so as to organize the compute nodes as a tree. In theexample of FIG. 5, dots represent compute nodes (102) of a SIMD machine,and the dotted lines (103) between the dots represent datacommunications links between compute nodes. The data communicationslinks are implemented with collective operations data communicationsadapters similar to the one illustrated for example in FIG. 3B, witheach node typically providing data communications to and from twochildren nodes and data communications to and from a parent node, withsome exceptions. Nodes in a binary tree may be characterized as a rootnode (202), branch nodes (204), and leaf nodes (206). The root node(202) has two children but no parent. The leaf nodes (206) each has aparent, but leaf nodes have no children. The branch nodes (204) each hasboth a parent and two children. The links and compute nodes are therebyorganized by this data communications network optimized for collectiveoperations into a binary tree (108). For clarity of explanation, thedata communications network of FIG. 5 is illustrated with only 31compute nodes, but readers will recognize that a data communicationsnetwork optimized for collective operations for use in executing MIMDprograms on a SIMD machine in accordance with embodiments of the presentinvention may contain only a few compute nodes or may contain thousandsof compute nodes.

In the example of FIG. 5, each node in the tree is assigned a unitidentifier referred to as a ‘rank’ (250). A node's rank uniquelyidentifies the node's location in the tree network for use in both pointto point and collective operations in the tree network. The ranks inthis example are assigned as integers beginning with 0 assigned to theroot node (202), 1 assigned to the first node in the second layer of thetree, 2 assigned to the second node in the second layer of the tree, 3assigned to the first node in the third layer of the tree, 4 assigned tothe second node in the third layer of the tree, and so on. For ease ofillustration, only the ranks of the first three layers of the tree areshown here, but all compute nodes in the tree network are assigned aunique rank.

For further explanation, FIG. 6 sets forth a functional block diagramillustrating an exemplary system for executing MIMD programs on a SIMDmachine according to embodiments of the present invention. The system ofFIG. 6 operates generally to execute MIMD programs (158) on a SIMDmachine (100) according to embodiments of the present invention bybooting the SIMD machine (100) in MIMD mode; executing by launcherprograms (135) a plurality of MIMD programs (158) on two or more of thecompute nodes (102) on the SIMD machine (100); and re-executing alauncher program (135) by an operating system on a compute node upontermination of the MIMD program executed by the launcher program.Booting the SIMD machine (100) in MIMD mode includes setting, inoperating systems on the compute nodes of the SIMD machine, flagsindicating MIMD operation; loading onto the compute nodes of the SIMDmachine a launcher program (135); initializing with link trainingsynchronous data communications among links of the network among computenodes in the SIMD machine; initializing, with a parallel processingbarrier, parallel operations among the compute nodes of the SIMDmachine; and executing a launcher program on each compute node in theSIMD machine.

The compute nodes (102) are coupled for data communications by severalindependent data communications networks including a high speed Ethernetnetwork (174), a Joint Test Action Group (‘JTAG’) network (104), acollective network (106) which is optimized for collective operations, apoint-to-point network (108) which is optimized for point to pointoperations among compute nodes, and a barrier network (109) which isoptimized for execution of parallel processing barriers. Each datacommunications network is implemented with data communications linksamong the compute nodes (102). The data communications links providedata communications for parallel operations among the compute nodes ofthe SIMD machine. Point-to-point network (108) is a synchronous datacommunications network that includes synchronous data communicationslinks connected among the compute nodes so as to organize the computenodes in a mesh or torus. Collective network (106) is a synchronous datacommunications network that includes synchronous data communicationslinks connected among the compute nodes so as to organize the computenodes in a tree structure.

The SIMD machine (100) includes a service node (116) coupled to thecompute nodes through the JTAG network (104). Service node (116)provides services common to pluralities of compute nodes, loadingprograms into the compute nodes, starting program execution on thecompute nodes, retrieving results of program operations on the computernodes, and so on. Service node (116) runs service applications (143) andcommunicates with users (128) through a service application interface(126) that runs on computer terminal (122). Service applications (143)that execute on the service node (116) include:

-   -   a control application (124), which is a module of computer        program instructions that loads launcher programs onto compute        nodes and administers error conditions detected on compute        nodes,    -   a scheduler (140), which is a module of computer program        instructions that schedules data processing jobs on the SIMD        machine, including installing SIMD programs on compute nodes and        passing MIMD jobs along to a MIMD dispatcher; and    -   a MIMD dispatcher (139), which is a module of computer program        instructions that installs MIMD programs on compute nodes when        the SIMD machine is booted in MIMD mode.

The service applications in this example are supported by a main jobqueue (141), a MIMD job programs table (142), and a MIMD job queue(138). The main job queue (141) is represented as table in this examplewith columns for a job identification code, a job type code, and acolumn specifying the number of compute nodes needed to execute a job.Each record in the main job queue (141) represents either a MIMD job ora SIMD job. Each SIMD job represents a single SIMD program that will runidentically on each compute node (102) in the SIMD machine (100) whenthe SIMD machine is booted in SIMD mode. Each MIMD job represents one ormore MIMD programs that will be executed on one or more compute nodes ofthe SIMD machine when the SIMD machine is booted in MIMD mode.

The main job queue (141) in this example is represented in a one-to-manydata modeling relationship with the MIMD job programs table using thejob identification code as a foreign key. Each SIMD job is implementedwith a single SIMD program, but a MIMD job, requiring no strictparallelism, no collective operations, no parallel processing barriers,can be composed of any number of individual MIMD programs which may beexecuted asynchronously with respect to one another. So in this example,the MIMD job identified by job code “J1” is composed of three MIMDprograms, “Prog1,” “Prog2,” and “Prog3.” Similarly, the MIMD jobidentified by job code “J2” is composed of four MIMD programs, “Prog4,”“Prog5,” “Prog6,” and “Prog7.”

The scheduler (140) only loads and executes SIMD jobs (146). Thescheduler is optimized to load the same program onto each and everycompute node of the SIMD machine, but loading a MIMD job requiresloading multiple separate, individual programs onto separate computenodes, a process for which the MIMD dispatcher is optimized. When thescheduler encounters a MIMD job in the main job queue, therefore, thescheduler hands that job off to the MIMD dispatcher, which then loadsand executes the MIMD job (145). The scheduler (140) hands off MIMD jobsto the MIMD dispatcher (130) by registering the jobs in the MIMD jobqueue (138), represented here as a table with two columns, a jobidentification and a representation of the number of compute nodesneeded for each MIMD job, where each record in the MIMD job queuerepresents a MIMD job to be dispatched for execution by the MIMDdispatcher (139). The MIMD dispatcher (139) dispatches MIMD jobs forexecution by communicating the name of MIMD programs comprising a MIMDjob to individual launcher programs running on individual compute nodes.

In the example of FIG. 6, there is no partitioning. When the SIMDmachine (100) of FIG. 6 is booted in SIMD mode, the entire machine isbooted in SIMD mode, and one SIMD program at a time will be run on allthe compute nodes of the machine. When the SIMD machine (100) of FIG. 6is booted in MIMD mode, the entire machine is booted in MIMD mode, andmultiple MIMD programs can then be run on any of the compute nodes ofthe machine. Note what happens, however, as the scheduler (140)schedules the jobs presently in the main job queue (141). The SIMDmachine (100) is booted in MIMD mode, and the scheduler (140) hands offjobs J1 and J2, which are MIMD jobs, to the MIMD dispatcher (139)through the MIMD job queue (138), and the MIMD dispatcher (139)dispatches the two MIMD jobs (145) for execution. The scheduler (140)then encounters the next job in the main job queue, J3, which is a SIMDjob. Now to run the next two jobs, J3 and J4, both of which are SIMDjobs, the entire SIMD machine (100) must be rebooted in SIMD mode.Similarly, when more MIMD jobs are to be run, the entire SIMD machinemust be again be rebooted in MIMD mode. And so on. The data processingarchitecture in the example of FIG. 6 is very powerful for applicationsthat are mostly or entirely SIMD—or mostly or entirely MIMD. Forapplications that require a combination of MIMD and SIMD jobs, however,an architecture with more flexibility is indicated.

For further explanation, FIG. 7 sets forth a functional block diagramillustrating a further exemplary system for executing MIMD programs on aSIMD machine according to embodiments of the present invention.Regarding the execution of a combination of MIMD jobs and SIMD jobs, thearchitecture represented by the example of FIG. 7 provides anadvancement in flexibility. The system of FIG. 7 operates generally toexecute MIMD programs (158) on a SIMD machine (100) according toembodiments of the present invention by establishing a SIMD partition(133) comprising a plurality of the compute nodes (102); booting theSIMD partition (133) in MIMD mode; executing by launcher programs (135)a plurality of MIMD programs (158) on two or more of the compute nodes(102) in the SIMD partition (133); and re-executing a launcher program(135) by an operating system on a compute node in the SIMD partitionupon termination of the MIMD program executed by the launcher program.Booting the SIMD partition (133) in MIMD mode includes setting, inoperating systems on the compute nodes of the SIMD partition, flagsindicating MIMD operation; loading onto the compute nodes of the SIMDpartition a launcher program; initializing with link trainingsynchronous data communications among links of the network among computenodes in the SIMD partition; initializing, with a parallel processingbarrier, parallel operations among the compute nodes of the SIMDpartition; and executing a launcher program on each compute node in theSIMD partition.

The compute nodes (102) are coupled for data communications by severalindependent data communications networks including a high speed Ethernetnetwork (174), a Joint Test Action Group (‘JTAG’) network (104), acollective network (106) which is optimized for collective operations, apoint-to-point network (108) which is optimized for point to pointoperations among compute nodes, and a barrier network (109) which isoptimized for execution of parallel processing barriers. Each datacommunications network is implemented with data communications linksamong the compute nodes (102). The data communications links providedata communications for parallel operations among the compute nodes ofthe SIMD partition. Point-to-point network (108) is a synchronous datacommunications network that includes synchronous data communicationslinks connected among the compute nodes so as to organize the computenodes of the SIMD partition in a mesh or torus. Collective network (106)is a synchronous data communications network that includes synchronousdata communications links connected among the compute nodes so as toorganize the compute nodes of the SIMD partition in a tree structure.

The SIMD machine (100) includes a service node (116) coupled to thecompute nodes through the JTAG network (104). Service node (116)provides services common to pluralities of compute nodes, loadingprograms into the compute nodes, starting program execution on thecompute nodes, retrieving results of program operations on the computernodes, and so on. Service node (116) runs service applications (143) andcommunicates with users (128) through a service application interface(126) that runs on computer terminal (122). Service applications (143)that execute on the service node (116) include:

-   -   a control application (124), which is a module of computer        program instructions that boots partitions, loads launcher        programs onto compute nodes in SIMD partitions booted in MIMD        mode, and administers error conditions detected on compute        nodes,    -   a scheduler (140), which is a module of computer program        instructions that schedules data processing jobs on the SIMD        machine, including installing SIMD programs on compute nodes and        passing MIMD jobs along to a MIMD dispatcher for execution on        SIMD partitions booted in MIMD mode; and    -   a MIMD dispatcher (139), which is a module of computer program        instructions that installs MIMD programs on compute nodes in        SIMD partitions booted in MIMD mode.

The service applications in this example are supported by a main jobqueue (141), a MIMD job programs table (142), and a MIMD job queue(138). The main job queue (141) is represented as table in this examplewith columns for a job identification code, a job type code, and acolumn specifying the number of compute nodes needed to execute a job.Each record in the main job queue (141) represents either a MIMD job ora SIMD job. Each SIMD job represents a single SIMD program that will runidentically on each compute node (102) in a SIMD partition booted inSIMD mode. Each MIMD job represents one or more MIMD programs that willbe executed on one or more compute nodes of a SIMD partition booted inMIMD mode.

The main job queue (141) in this example is represented in a one-to-manydata modeling relationship with the MIMD job programs table (142) usingthe job identification code as a foreign key. Each SIMD job isimplemented with a single SIMD program, but a MIMD job, requiring nostrict parallelism, no collective operations, no parallel processingbarriers, can be composed of any number of individual MIMD programswhich may be executed asynchronously with respect to one another. So inthis example, the MIMD job identified by job code “J1” is composed ofthree MIMD programs, “Prog1,” “Prog2,” and “Prog3.” Similarly, the MIMDjob identified by job code “J2” is composed of four MIMD programs,“Prog4,” “Prog5,” “Prog6,” and “Prog7.”

The scheduler (140) only loads and executes SIMD jobs (146). Thescheduler is optimized to load the same SIMD program onto each and everycompute node of the SIMD machine, but loading a MIMD job requiresloading multiple separate, individual programs onto separate computenodes, a process for which the MIMD dispatcher is optimized. When thescheduler (140) encounters a MIMD job in the main job queue (141),therefore, the scheduler hands that job off to the MIMD dispatcher(139), which then loads and executes the MIMD job (145). The scheduler(140) hands off MIMD jobs to the MIMD dispatcher (130) by registeringthe jobs in the MIMD job queue (138), represented here as a table withtwo columns, a job identification and a representation of the number ofcompute nodes needed for each MIMD job, where each record in the MIMDjob queue represents a MIMD job to be dispatched for execution by theMIMD dispatcher (139). The MIMD dispatcher (139) dispatches MIMD jobsfor execution by communicating the name of MIMD programs comprising aMIMD job individual launcher programs running on individual computenodes in a SIMD partition booted in MIMD mode (133).

In the example of FIG. 7, the SIMD machine supports partitioning, andeach partition can be booted either in SIMD mode or in MIMD mode. When aSIMD partition (132) is booted in SIMD mode, the entire partition isbooted in SIMD mode, and one SIMD program at a time will be run on allthe compute nodes of the partition. When a SIMD partition (133) isbooted in MIMD mode, the entire partition is booted in MIMD mode, andmultiple MIMD programs can then be run on any of the compute nodes ofthe partition. A control application (124) according to embodiments ofthe present invention can establish on a SIMD machine a SIMD partitionbooted in MIMD mode, with a SIMD partition booted in SIMD mode runningsimultaneously with the SIMD partition booted in MIMD mode. On such aSIMD machine, multiple MIMD applications may be run simultaneously inone partition while SIMD applications are run in another partition, allon the same machine at the same time.

Note what happens in the example of FIG. 7 as the scheduler (140)schedules the jobs presently in the main job queue (141). One SIMDpartition (133) is booted in MIMD mode, and the scheduler (140) handsoff jobs J1 and J2, which are MIMD jobs, to the MIMD dispatcher (139)through the MIMD job queue (138), and the MIMD dispatcher (139)dispatches the two MIMD jobs (145) for execution in the SIMD partition(133) booted in MIMD mode. The scheduler (140) then encounters the nextjob in the main job queue, J3, which is a SIMD job. Now to run the nexttwo jobs, J3 and J4, both of which are SIMD jobs, there is no need toreboot the entire SIMD machine. On the contrary, in this example, thescheduler (140) loads and executes J3 immediately on the SIMD partition(132) booted in SIMD mode, and, as soon as J3 terminates, the schedulerthen promptly loads and executes J4 on the SIMD partition (132) bootedin SIMD mode. J3 and J4 can both execute simultaneously with MIMDapplications on the SIMD partition (133) booted in MIMD mode. Given asufficient number of available compute nodes on the SIMD machine, thecontrol application (124) can boot another SIMD partition in SIMD mode,and both J3 and J4 can be run at the same time. Similarly, givensufficient demand and sufficient availability of compute nodes, morethan one SIMD partition can be booted in MIMD mode also.

For further explanation, FIG. 8 sets forth a flow chart illustrating anexemplary method for executing MIMD programs on a SIMD machine accordingto embodiments of the present invention. The method of FIG. 8 is carriedout on a SIMD machine (100) similar to the SIMD machines describedabove. The SIMD machine includes a number of compute nodes (102), whereeach compute node is capable of executing only a single thread ofexecution. The compute nodes are initially configured exclusively forSIMD operations. The SIMD machine includes at least one datacommunications network (104, 106, 108, 109, 174 on FIG. 1) that includessynchronous data communications links among the compute nodes.

The method of FIG. 8 includes establishing (302) a SIMD partition (133)that includes a plurality of the compute nodes, with the compute nodesin the SIMD partition (133) electronically isolated from compute nodesin other partitions (132) of the SIMD machine (100). The compute nodesin the partition (133) are coupled to one another through links of anetwork (106 or 108 on FIG. 1) for synchronous data communications forparallel SIMD operations among the compute nodes in the SIMD partition.

The method of FIG. 8 also includes booting (304) the SIMD partition inMIMD mode. Booting (304) the SIMD partition in MIMD mode includessetting (306), in operating systems on the compute nodes of the SIMDpartition, flags indicating MIMD operation. Such flags are Boolean dataelements, and setting them means setting them to TRUE. Booting (304) theSIMD partition in MIMD mode also includes loading (307) onto the computenodes of the SIMD partition a launcher program (135), one instance ofthe launcher program on each compute node in the SIMD partition (133).

Booting (304) the SIMD partition in MIMD mode also includes initializing(308) with link training synchronous data communications among links ofthe network among compute nodes in the SIMD partition. Link training isan initialization process for links in a high performance network thatuses specific data packet types known as training sequences to enableeach link to determine its link width, polarity, device presence, andalso to detect problems in the link.

Booting (304) the SIMD partition in MIMD mode also includes initializing(310), with a parallel processing barrier, parallel operations among thecompute nodes of the SIMD partition. A parallel processing barrier is aparallel processing function, typically implemented as a member of amessage passing library such as MPI, that synchronizes operation of allprocesses executing in a SIMD partition. All processes in the partitioncontain a call to a barrier at a point in processing where all theprocesses need to be synchronized. Each process that calls the barrierfunction waits to continue processing until all of the processes in thepartition have called the barrier function. It is not uncommon for highperformance SIMD machines to implement barriers with special hardwaresupport, as is the case for the SIMD machine described above withreference to FIG. 1. That SIMD machine has an independent datacommunication network (109) dedicated to the execution of barriers.

Booting (304) the SIMD partition in MIMD mode also includes executing(312) a launcher program on each compute node in the SIMD partition. Themethod of FIG. 6 also includes executing (314) by launcher programs(135) a plurality of MIMD programs (158) on two or more of the computenodes in the SIMD partition. Each MIMD program autonomously executesdifferent instructions on different data. Such execution of a MIMDprogram by a launcher program wipes out the launcher program, replacingthe launcher program with the MIMD program in process address space incomputer memory of a compute nodes. The method of FIG. 6 also includesre-executing (316) a launcher program by an operating system on acompute node in the SIMD partition upon termination of the MIMD programexecuted by the launcher program.

For further explanation, FIG. 9 sets forth a flow chart illustrating afurther exemplary method for executing MIMD programs on a SIMD machineaccording to embodiments of the present invention. The method of FIG. 9is similar to the method of FIG. 8, including as it does establishing(302) a SIMD partition (133), booting (304) the SIMD partition in MIMDmode, executing (314) by launcher programs (135) MIMD programs (158) oncompute nodes in the SIMD partition, and re-executing (316) a launcherprogram upon termination of the MIMD program executed by the launcherprogram, all of which function as described above. In the method of FIG.9, however, loading (307) a launcher program includes loading (309) alauncher program by a control application (124 on FIG. 1) on a servicenode (116 on FIG. 1) through a service network such as a JTAG network(104 on FIG. 1) through input/output nodes (110, 114 on FIG. 1) througha collective network (106 on FIG. 1) into compute nodes (102) of theSIMD partition (133) booted in MIMD mode.

The method of claim 9 also includes communicating (320), by a MIMDdispatcher (139 on FIGS. 1 and 7) to a launcher program on a computenode in the SIMD partition booted (133) in MIMD mode, the name of a MIMDprogram to execute by the launcher. The launcher then uses the MIMDprogram name to retrieve the MIMD program through an i/o node (110 onFIG. 1) from a disk drive (118 on FIG. 1) and install the MIMD programin process address space in the RAM of a compute node. The name of theMIMD program may include a pathname helping to locate the MIMD programon disk.

The method of claim 9 also includes establishing (322) on the SIMDmachine (100) a SIMD partition (132) booted in SIMD mode, with the SIMDpartition booted in SIMD mode running simultaneously with the SIMDpartition (133) booted in MIMD mode.

For further explanation, FIG. 10 sets forth a flow chart illustrating afurther exemplary method for executing MIMD programs on a SIMD machineaccording to embodiments of the present invention. The method of FIG. 10is similar to the method of FIG. 8, including as it does establishing(302) a SIMD partition (133), booting (304) the SIMD partition in MIMDmode, executing (314) by launcher programs (135) MIMD programs (158) oncompute nodes in the SIMD partition, and re-executing (316) a launcherprogram upon termination of the MIMD program executed by the launcherprogram, all of which function as described above. The method of FIG.10, however, also includes detecting (322) by a compute node (102) aprocessing error. This can be any processing error, a memory fault, acache fault, a processor fault, and so on, as will occur to those ofskill in the art. The method of FIG. 10 also includes communicating(324) by the compute node through a service network to a controlapplication on a service node the existence of the processing error. Theservice network can a JTAG network (104 on FIG. 1), for example. Themethod of FIG. 10 also includes booting (326), by the controlapplication without affecting operations of other compute nodes, thecompute node in MIMD mode. This boot is in effect an error recoverytechnique. In the method of FIG. 10, booting (326) the compute node inMIMD mode includes:

-   -   setting (328), in an operating system on the compute node, a        flag (136 on FIG. 2) indicating MIMD operation;    -   setting (330), in an operating system on the compute node, a        flag (137 on FIG. 2) indicating that the current boot of the        compute node is a reboot; and    -   loading and executing (332) a launcher program on the compute        node.

In the method of FIG. 10, booting (326) the compute node in MIMD modeomits (334) the initializing of synchronous data communications on thenetwork with link training and the initializing of parallel operationsamong the compute nodes with a parallel processing barrier. Linktraining and initialization with parallel processing barriers areprocesses included in an initial boot of a SIMD partition because of theunderlying SIMD architecture. Link training and initialization withparallel processing barriers are not needed for a reboot of anindividual compute node, however, in a SIMD partition booted in MIMDmode, because link training and initialization with parallel processingbarriers for the underlying SIMD architecture have already beenperformed. It is the set reboot flag (137 on FIG. 2) that advises theoperating system in the compute node to omit the link training andinitialization with parallel processing barriers.

Exemplary embodiments of the present invention are described largely inthe context of a fully functional computer system for executing MIMDprograms on a SIMD machine. Readers of skill in the art will recognize,however, that the present invention also may be embodied in a computerprogram product disposed on computer readable, signal bearing media foruse with any suitable data processing system. Such signal bearing mediamay be transmission media or recordable media for machine-readableinformation, including magnetic media, optical media, or other suitablemedia. Examples of recordable media include magnetic disks in harddrives or diskettes, compact disks for optical drives, magnetic tape,and others as will occur to those of skill in the art. Examples oftransmission media include telephone networks for voice communicationsand digital data communications networks such as, for example,Ethernets™ and networks that communicate with the Internet Protocol andthe World Wide Web.

Persons skilled in the art will immediately recognize that any computersystem having suitable programming means will be capable of executingthe steps of the method of the invention as embodied in a programproduct. Persons skilled in the art will recognize immediately that,although some of the exemplary embodiments described in thisspecification are oriented to software installed and executing oncomputer hardware, nevertheless, alternative embodiments implemented asfirmware or as hardware are well within the scope of the presentinvention.

It will be understood from the foregoing description that modificationsand changes may be made in various embodiments of the present inventionwithout departing from its true spirit. The descriptions in thisspecification are for purposes of illustration only and are not to beconstrued in a limiting sense. The scope of the present invention islimited only by the language of the following claims.

1. A method of executing Multiple Instructions Multiple Data (‘MIMD’)programs on a Single Instruction Multiple Data (‘SIMD’) machine, theSIMD machine comprising a plurality of compute nodes, each compute nodecapable of executing only a single thread of execution, the computenodes initially configured exclusively for SIMD operations, the SIMDmachine further comprising a data communications network, the networkcomprising synchronous data communications links among the computenodes, the method comprising: establishing a SIMD partition comprising aplurality of the compute nodes, the compute nodes in the SIMD partitionelectronically isolated from compute nodes in other partitions of theSIMD machine and coupled to one another through links of the network forsynchronous data communications for parallel SIMD operations among thecompute nodes in the SIMD partition; booting the SIMD partition in MIMDmode, including: setting, in operating systems on the compute nodes ofthe SIMD partition, flags indicating MIMD operation; loading onto thecompute nodes of the SIMD partition a launcher program; initializingwith link training synchronous data communications among links of thenetwork among compute nodes in the SIMD partition; initializing, with aparallel processing barrier, parallel operations among the compute nodesof the SIMD partition, and executing a launcher program on each computenode in the SIMD partition; executing by launcher programs a pluralityof MIMD programs on two or more of the compute nodes in the SIMDpartition, including replacing the launcher programs with the MIMDprograms in process address space in computer memory of the computenodes, each MIMD program autonomously executing different instructionson different data; and re-executing a launcher program by an operatingsystem on a compute node in the SIMD partition upon termination of theMIMD program executed by the launcher program.
 2. The method of claim 1further comprising communicating, by a dispatcher to a launcher programon a compute node in the SIMD partition booted in MIMD mode, the name ofa MIMD program to execute by the launcher.
 3. The method of claim 1wherein loading a launcher program further comprises loading a launcherprogram by a control application on a service node through a servicenetwork through input/output nodes through a collective network intocompute nodes of the SIMD partition booted in MIMD mode.
 4. The methodof claim 1 further comprising establishing on the SIMD machine a SIMDpartition booted in SIMD mode, with the SIMD partition booted in SIMDmode running simultaneously with the SIMD partition booted in MIMD mode.5. The method of claim 1 further comprising: detecting by a compute nodea processing error; communicating by the compute node through a servicenetwork to a control application on a service node the existence of theprocessing error; and booting, by the control application withoutaffecting operations of other compute nodes, the compute node in MIMDmode, the booting including: setting, in an operating system on thecompute node, a flag indicating MIMD operation; setting, in an operatingsystem on the compute node, a flag indicating that the current boot ofthe compute node is a reboot; loading and executing a launcher programon the compute node; omitting the initializing of synchronous datacommunications on the network with link training and the initializing ofparallel operations among the compute nodes with a parallel processingbarrier.
 6. Apparatus for executing Multiple Instructions Multiple Data(‘MIMD’) programs on a Single Instruction Multiple Data (‘SIMD’)machine, the SIMD machine comprising a plurality of compute nodes, eachcompute node capable of executing only a single thread of execution, thecompute nodes initially configured exclusively for SIMD operations, theSIMD machine further comprising a data communications network, thenetwork comprising synchronous data communications links among thecompute nodes, the apparatus comprising a computer processor, a computermemory operatively coupled to the computer processor, the computermemory having disposed within it computer program instructions capableof: establishing a SIMD partition comprising a plurality of the computenodes, the compute nodes in the SIMD partition electronically isolatedfrom compute nodes in other partitions of the SIMD machine and coupledto one another through links of the network for synchronous datacommunications for parallel SIMD operations among the compute nodes inthe SIMD partition; booting the SIMD partition in MIMD mode, including:setting, in operating systems on the compute nodes of the SIMDpartition, flags indicating MIMD operation; loading onto the computenodes of the SIMD partition a launcher program; initializing with linktraining synchronous data communications among links of the networkamong compute nodes in the SIMD partition; initializing, with a parallelprocessing barrier, parallel operations among the compute nodes of theSIMD partition, and executing a launcher program on each compute node inthe SIMD partition; executing by launcher programs a plurality of MIMDprograms on two or more of the compute nodes in the SIMD partition,including replacing the launcher programs with the MIMD programs inprocess address space in computer memory of the compute nodes, each MIMDprogram autonomously executing different instructions on different data;and re-executing a launcher program by an operating system on a computenode in the SIMD partition upon termination of the MIMD program executedby the launcher program.
 7. The apparatus of claim 6 further comprisingcomputer program instructions capable of communicating, by a dispatcherto a launcher program on a compute node in the SIMD partition booted inMIMD mode, the name of a MIMD program to execute by the launcher.
 8. Theapparatus of claim 6 wherein loading a launcher program furthercomprises loading a launcher program by a control application on aservice node through a service network through input/output nodesthrough a collective network into compute nodes of the SIMD partitionbooted in MIMD mode.
 9. The apparatus of claim 6 further comprisingcomputer program instructions capable of establishing on the SIMDmachine a SIMD partition booted in SIMD mode, with the SIMD partitionbooted in SIMD mode running simultaneously with the SIMD partitionbooted in MIMD mode.
 10. The apparatus of claim 6 further comprisingcomputer program instructions capable of: detecting by a compute node aprocessing error; communicating by the compute node through a servicenetwork to a control application on a service node the existence of theprocessing error; and booting, by the control application withoutaffecting operations of other compute nodes, the compute node in MIMDmode, the booting including: setting, in an operating system on thecompute node, a flag indicating MIMD operation; setting, in an operatingsystem on the compute node, a flag indicating that the current boot ofthe compute node is a reboot; loading and executing a launcher programon the compute node; omitting the initializing of synchronous datacommunications on the network with link training and the initializing ofparallel operations among the compute nodes with a parallel processingbarrier.
 11. A computer program product for executing MultipleInstructions Multiple Data (‘MIMD’) programs on a Single InstructionMultiple Data (‘SIMD’) machine, the SIMD machine comprising a pluralityof compute nodes, each compute node capable of executing only a singlethread of execution, the compute nodes initially configured exclusivelyfor SIMD operations, the SIMD machine further comprising a datacommunications network, the network comprising synchronous datacommunications links among the compute nodes, the computer programproduct disposed in a computer readable, signal bearing medium, thecomputer program product comprising computer program instructionscapable of: establishing a SIMD partition comprising a plurality of thecompute nodes, the compute nodes in the SIMD partition electronicallyisolated from compute nodes in other partitions of the SIMD machine andcoupled to one another through links of the network for synchronous datacommunications for parallel SIMD operations among the compute nodes inthe SIMD partition; booting the SIMD partition in MIMD mode, including:setting, in operating systems on the compute nodes of the SIMDpartition, flags indicating MIMD operation; loading onto the computenodes of the SIMD partition a launcher program; initializing with linktraining synchronous data communications among links of the networkamong compute nodes in the SIMD partition; initializing, with a parallelprocessing barrier, parallel operations among the compute nodes of theSIMD partition, and executing a launcher program on each compute node inthe SIMD partition; executing by launcher programs a plurality of MIMDprograms on two or more of the compute nodes in the SIMD partition,including replacing the launcher programs with the MIMD programs inprocess address space in computer memory of the compute nodes, each MIMDprogram autonomously executing different instructions on different data;and re-executing a launcher program by an operating system on a computenode in the SIMD partition upon termination of the MIMD program executedby the launcher program.
 12. The computer program product of claim 11further comprising computer program instructions capable ofcommunicating, by a dispatcher to a launcher program on a compute nodein the SIMD partition booted in MIMD mode, the name of a MIMD program toexecute by the launcher.
 13. The computer program product of claim 11wherein loading a launcher program further comprises loading a launcherprogram by a control application on a service node through a servicenetwork through input/output nodes through a collective network intocompute nodes of the SIMD partition booted in MIMD mode.
 14. Thecomputer program product of claim 11 further comprising computer programinstructions capable of establishing on the SIMD machine a SIMDpartition booted in SIMD mode, with the SIMD partition booted in SIMDmode running simultaneously with the SIMD partition booted in MIMD mode.15. The computer program product of claim 11 further comprising computerprogram instructions capable of: detecting by a compute node aprocessing error; communicating by the compute node through a servicenetwork to a control application on a service node the existence of theprocessing error; and booting, by the control application withoutaffecting operations of other compute nodes, the compute node in MIMDmode, the booting including: setting, in an operating system on thecompute node, a flag indicating MIMD operation; setting, in an operatingsystem on the compute node, a flag indicating that the current boot ofthe compute node is a reboot; loading and executing a launcher programon the compute node; omitting the initializing of synchronous datacommunications on the network with link training and the initializing ofparallel operations among the compute nodes with a parallel processingbarrier.
 16. A method of executing Multiple Instructions Multiple Data(‘MIMD’) programs on a Single Instruction Multiple Data (‘SIMD’)machine, the SIMD machine comprising a plurality of compute nodes, eachcompute node capable of executing only a single thread of execution, thecompute nodes initially configured exclusively for SIMD operations, theSIMD machine further comprising a data communications network, thenetwork comprising synchronous data communications links among thecompute nodes, the method comprising: booting the SIMD machine in MIMDmode, including: setting, in operating systems on the compute nodes,flags indicating MIMD operation; loading onto the compute nodes alauncher program; initializing, with link training, synchronous datacommunications among links of the network among compute nodes in theSIMD partition; initializing, with a parallel processing barrier,parallel operations among the compute nodes; and executing a launcherprogram on each compute node; executing by launcher programs a pluralityof MIMD programs on two or more of the compute nodes, includingreplacing the launcher programs with the MIMD programs in processaddress space in computer memory of the compute nodes, each MIMD programautonomously executing different instructions on different data; andre-executing a launcher program by an operating system upon terminationof the MIMD program executed by the launcher program.
 17. The method ofclaim 1 further comprising communicating by a dispatcher to a launcherprogram on a compute node the name of a MIMD program to execute by thelauncher.
 18. The method of claim 1 wherein loading a launcher programfurther comprises loading a launcher program by a control application ona service node through a service network through i/o nodes through acollective network into compute nodes.
 19. The method of claim 1 furthercomprising establishing on the SIMD machine a SIMD partition booted inSIMD mode and a SIMD partition booted in MIMD mode, with the SIMDpartition booted in SIMD mode running simultaneously with the SIMDpartition booted in MIMD mode.
 20. The method of operating claim 1further comprising: detecting by a compute node a processing error;communicating by the compute node through a service (JTAG) network to aservice application on a service node the existence of the processingerror; and booting the compute node in MIMD mode, including setting inan operating system on the compute node a flag indicating MIMDoperation, further including setting in an operating system on thecompute node a flag indicating that the current boot of the compute nodeis a reboot, further including loading a launcher program on the computenode, omitting the initializing of synchronous data communications onthe network with link training, and omitting the initializing ofparallel operations among the compute nodes with a parallel processingbarrier, the booting implemented without affecting operations of othercompute nodes.
 21. Apparatus for executing Multiple InstructionsMultiple Data (‘MIMD’) programs on a Single Instruction Multiple Data(‘SIMD’) machine, the SIMD machine comprising a plurality of computenodes, each compute node capable of executing only a single thread ofexecution, the compute nodes initially configured exclusively for SIMDoperations, the SIMD machine further comprising a data communicationsnetwork, the network comprising synchronous data communications linksamong the compute nodes, the apparatus comprising a computer processor,a computer memory operatively coupled to the computer processor, thecomputer memory having disposed within it computer program instructionscapable of: booting the SIMD machine in MIMD mode, including: setting,in operating systems on the compute nodes, flags indicating MIMDoperation; loading onto the compute nodes a launcher program;initializing, with link training, synchronous data communications amonglinks of the network among compute nodes in the SIMD partition;initializing, with a parallel processing barrier, parallel operationsamong the compute nodes; and executing a launcher program on eachcompute node; executing by launcher programs a plurality of MIMDprograms on two or more of the compute nodes, including replacing thelauncher programs with the MIMD programs in process address space incomputer memory of the compute nodes, each MIMD program autonomouslyexecuting different instructions on different data; and re-executing alauncher program by an operating system upon termination of the MIMDprogram executed by the launcher program.
 22. The apparatus of claim 21further comprising computer program instructions capable ofcommunicating by a dispatcher to a launcher program on a compute nodethe name of a MIMD program to execute by the launcher.
 23. The apparatusof claim 21 wherein loading a launcher program further comprises loadinga launcher program by a control application on a service node through aservice network through i/o nodes through a collective network intocompute nodes.
 24. The apparatus of claim 21 further comprising computerprogram instructions capable of establishing on the SIMD machine a SIMDpartition booted in SIMD mode and a SIMD partition booted in MIMD mode,with the SIMD partition booted in SIMD mode running simultaneously withthe SIMD partition booted in MIMD mode.
 25. The apparatus of claim 21further comprising computer program instructions capable of: detectingby a compute node a processing error; communicating by the compute nodethrough a service (JTAG) network to a service application on a servicenode the existence of the processing error; and booting the compute nodein MIMD mode, including setting in an operating system on the computenode a flag indicating MIMD operation, further including setting in anoperating system on the compute node a flag indicating that the currentboot of the compute node is a reboot, further including loading alauncher program on the compute node, omitting the initializing ofsynchronous data communications on the network with link training, andomitting the initializing of parallel operations among the compute nodeswith a parallel processing barrier, the booting implemented withoutaffecting operations of other compute nodes.
 26. A computer programproduct for executing Multiple Instructions Multiple Data (‘MIMD’)programs on a Single Instruction Multiple Data (‘SIMD’) machine, theSIMD machine comprising a plurality of compute nodes, each compute nodecapable of executing only a single thread of execution, the computenodes initially configured exclusively for SIMD operations, the SIMDmachine further comprising a data communications network, the networkcomprising synchronous data communications links among the computenodes, the computer program product disposed in a computer readable,signal bearing medium, the computer program product comprising computerprogram instructions capable of: booting the SIMD machine in MIMD mode,including: setting, in operating systems on the compute nodes, flagsindicating MIMD operation; loading onto the compute nodes a launcherprogram; initializing, with link training, synchronous datacommunications among links of the network among compute nodes in theSIMD partition; initializing, with a parallel processing barrier,parallel operations among the compute nodes; and executing a launcherprogram on each compute node; executing by launcher programs a pluralityof MIMD programs on two or more of the compute nodes, includingreplacing the launcher programs with the MIMD programs in processaddress space in computer memory of the compute nodes, each MIMD programautonomously executing different instructions on different data; andre-executing a launcher program by an operating system upon terminationof the MIMD program executed by the launcher program.
 27. The computerprogram product of claim 26 further comprising computer programinstructions capable of communicating by a dispatcher to a launcherprogram on a compute node the name of a MIMD program to execute by thelauncher.
 28. The computer program product of claim 26 wherein loading alauncher program further comprises loading a launcher program by acontrol application on a service node through a service network throughi/o nodes through a collective network into compute nodes.
 29. Thecomputer program product of claim 26 further comprising computer programinstructions capable of establishing on the SIMD machine a SIMDpartition booted in SIMD mode and a SIMD partition booted in MIMD mode,with the SIMD partition booted in SIMD mode running simultaneously withthe SIMD partition booted in MIMD mode.
 30. The computer program productof claim 26 further comprising computer program instructions capable of:detecting by a compute node a processing error; communicating by thecompute node through a service (JTAG) network to a service applicationon a service node the existence of the processing error; and booting thecompute node in MIMD mode, including setting in an operating system onthe compute node a flag indicating MIMD operation, further includingsetting in an operating system on the compute node a flag indicatingthat the current boot of the compute node is a reboot, further includingloading a launcher program on the compute node, omitting theinitializing of synchronous data communications on the network with linktraining, and omitting the initializing of parallel operations among thecompute nodes with a parallel processing barrier, the bootingimplemented without affecting operations of other compute nodes.